Co-investments - Summary of Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 1,045,059	$ 1,161,275
Total operating co investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	693,633	781,905
Membership Interest In CPPIB [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 461,872	422,068
Membership Interest In CPPIB [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	50.00%
Membership Interest In CPPIB [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	55.00%
Membership interest in Wesco I, III, and IV [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 180,005	180,687
Limited partnership interest in partnership investments (as a percent)	50.00%
Membership Interest In Palm Valley [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 0	68,396
Limited partnership interest in partnership investments (as a percent)	50.00%
Membership interest in BEXAEW [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 46,728	47,963
Limited partnership interest in partnership investments (as a percent)	50.00%
BEX II [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ (36,025)	19,078
Limited partnership interest in partnership investments (as a percent)	50.00%
Membership In Other [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 41,053	43,713
Membership In Other [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	50.00%
Membership In Other [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	55.00%
Total development co investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 126,119	157,317
Total development co investments [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	50.00%
Total development co investments [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Limited partnership interest in partnership investments (as a percent)	55.00%
Total preferred interest investments [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 225,307	222,053
Total preferred interest investments [Member] | Investments in Majority-owned Subsidiaries [Member]
Schedule of Equity Method Investments [Line Items]
Co-investments	$ 20,700	$ 35,900